This invention relates generally to pipettes. More particularly the present invention relates to piston seals for pipettes.
Air displacement pipettes are widely used to transfer fluid samples in bioscience research, pharmaceutical manufacturing, and clinical analysis. The accuracy with which fluid is transferred is often critical to the outcome of the application. Failure to deliver fluid volumes accurately is a major concern for applications that require precise fluid volume transfer. Pipette failure usually occurs gradually with time and the frequency of pipette usage. Thus pipette failure may often be discovered too late to enable a quick and economical remedy. Users must therefore increase the frequency of pipette testing and calibration in order to assure continued fluid dispensing accuracy.
FDA registered companies adopt quality control procedures that require pipettes to be evaluated, maintained and recalibrated routinely at least every 6 months. Non-FDA registered institutions typically perform similar recalibration procedures every 12-months, or sooner. Most pipette manufacturers usually recommend that pipettes be serviced every 12 months. According to a recent technical report published by a leading U.S pipette manufacturer, pipettes tested on a routine 12-month basis exhibited a 20% failure rate for accurate volumetric delivery. The same report also stated that 60% of pipette failure is due to failure of the piston seal. Failure of the piston itself accounted for another 25% of the total and 15% was due to body failure. To reduce the failure rate, the report recommended replacing the piston seal every 6 months. It was further recommended that the piston and body be replaced every 3 years to ensure pipette reliability.
Failure of the seal can be attributed to a combination of 1) wearing of the seal with repeated use (abrasion); 2) separation of the seal from the piston over time due to “cold flow” or creep, and 3) the elasticity characteristics of the seal material. Although all three of these factors contribute to seal failure, the wearing of the seal, or its abrasion resistance, has been thought to be the most significant factor.